Transformer apparatus



April 15, 1958 E. G. JOHNSON 2,831,164

TRANSFORMER APPARATUS I Filed Nov. 25,1953 5 Sheets-Sheet 1 F I16; I

A ril 15, 1958 E. G. JOHNSON 2,831,164

TRANSFORMER APPARATUS Filed Nov. 23, 1953 5 Sheets-Sheet 2 NTOR April 15, 1958 E. G. JOHNSON 2,831,164

' TRANSFORMER APPARATUS Filed Nov. 23, 1953 v 5 Sheets-Sheet 3 IN V EN TOR.

5 Sheets-Sheet 4 Filed Nov. 25, 1953 INVENTOR.

April 15, 1953 E. G. JOHNSON 2,831,164

TRANSFORMER APPARATUS 5 Shets-Sheet 5 Filed Nov. 23, 1953 IN VEN TOR.

United States Patent TRANSFORMER APPARATUS Ervin G. Johnson, Oakland, Calif., assignor to Eleanorde Haas Johnson, Oakland, Calif.

Application November 23, 1953, Serial No. 393,667

7 Claims. (Cl. 324-127) This invention relates to alternating current measurement and particularly to current measurement through the use of current transformers.

This application is a continuation-in-part of application Serial Number 7 30,326, filed February 24, 1947, now abandoned.

Current transformers are generally made to transform currents of a particular range or ranges of values. For currents up to approximately two hundred amperes a multiple turn primary winding is generally employed and above this value a single turn primary winding is adequate although when a single turn primary is usable different transformers are required to cover the various ranges of current since the calibration curves over different ranges for a single transformer are undesirable except for one range. Thus, a different transformer is generally required for the precise measurement of currents in the i500 ampere range than is employed for similar accuracy in the 500 ampere range. This is because the ratio and phase angle of a transformer varies with the induction and hence with the value of current producing the induction.

With the multiple turn primary windings the design is such that the induction in the core is kept within certain limits for various ranges of primary currents by changing the number of primary turns in inverse ratio to the number of amperes to be measured so that the ampereturus product on the primary has a range of values which is fixed between zero and a definite maximum value irrespective of the value of the current impressed on the chosen number of primary turns. It has heretofore been possible to construct a single current transformer for using a single turn primary, whose accuracy is acceptable in the range below 200 amperes. This is a generally used minimum value for which a single turn primary winding may be designed, and for such transformers a number of primary taps are provided by the use of which currents up to fifty amperes may be measured, the range from fifty to two hundred amperes being covered by four, three, two, and one turns of an inserted or cable primary.

By this invention the range of accuracy of any such transformer extends to values of current indefinitely higher than the value permitted by any one single turn primary winding design. I do this by arranging a primary winding on the core so that no matter how high the current measured may be, connections may be made sothat such current will produce no more than a fixed maximum of induction in the core. This limit is in contradistinction to the limit heretofore imposed, which was that the induction should never be less than a fixed minimum in order to obtain sufiicient energy to drive the metering apparatus. By this invention only a fractional part of the current measured is effective to produce induction in the core. When the fraction is made sufficiently small, the maximum induction may be maintained at a fixed value.

The fractional part of the current measured which is effective to produce induction is a substantially constant fraction irrespective of the value of the current measured by any particular connection of the apparatus. Therefore the measure of the fraction is a measure of the whole and the meter may be sealed in terms of the primary current.

It is accordingly the main object of this invention to extend the effectiveness of any particular current transformer to measure currents over wider ranges of values.

Although particularly intended to extend instrument current transformer effectiveness, the principles of this invention are applicable in other situations where a fraction of the primary current is employed to useful end. Thus in a relay transformer the invention will also be found useful, as will be clear to those skilled in the art.

Other'advantages of the invention will become ap parent from a consideration of the following specification wherein reference is made to the accompanying drawing for an illustration of one embodiment of the invention, and in which:

Fig. 1 is a schematic and fragmentary view partially in section;

Fig. 2 is a schematic view of another embodiment;

' Pig. 3 is a diagram of a further modification of the invention;

Fig. 4 is a view of a transformer similar to that of Fig. 1 but with an improvement in the terminal structure specifically illustrated in detail;

Fig. 5 is an illustration of an improved embodiment of the particular form illustrated in Fig. 3; and

Fig. 6 illustrates the application of the invention in extended form as a part of a bus bar structure.

In Fig. l the transformer comprises a ring core 10 about which there is threaded a primary winding 12 and a secondary winding 14. The secondary winding 14 is a conventional one, connected to a suitable ammeter 16. The primary winding shown is a single copper bar formed in a closed figure of eight as shown, and is provided with a terminal P at one end and one or more terminals M, M, etc., at the other end. Two current paths B and C are thereby provided between M and P. Current a entering at M divides and the two parts b and 0 pass through the paths B and C and out at terminal P. It will be observed that the currents b and 0 pass through the hole in the core 10 in opposite directions. The induction in 1 the ring core 10 is therefore due to only the difference between the values of the currents b and 0. By suitably roportioning the impedances of the two paths B and C the difference between the currents b and c is made any desired positive, zero, or negative value less than the larger, and any corresponding desired fractional part of the total current a. This may be done by choosing the point of entry of the current at M, or M, etc. Thus, as shown in Fig. l, the impedance between M and P along path B is slightly less than along path C; for example, let it be considered that the winding 12 is of a single conductor of uniform section and specific linear resistance. So, if the impedances of paths B and C from M to P are in the ratio 99/101 the effective value of the current of 1000 amperes, a, in circuit A is given by the expression:

101 plus 99 which equal ten amperes to produce induction in core 10. The magneto-motive force is likewise ten ampere turns. he ammeter 16 is preferably scaled to show ten amperes when 1000 amperes are flowing in the primary, and the readings of the scale may be multiplied by 100 to obtain the value of current a If the current a to be measured be of the order of five hundred amperes, another terminal, as M is arranged so that the ratio of impedance between M and P along 3 the respective paths B and C is 98/102. Then when the current is 500 amperes, the effective induction current is:

10298 102 plus 98 which equals ten amperes, and the meter 16 indicates ten amperes as before, the multiplier now being fifty instead of 100.

In Fig. 2 the shape of the primary winding 12 is somewhat altered so that the terminals Mo, M3, M3, M 4, and M4 are symmetrically related to the core. The ammeter 16 is chosen to read in portions of 1, as in percent, and its reading is directly multipled against a figure opposite the terminal connected to current path A. Thus, when M3 and P areconnected to circuit A, the reading of the 'ammeter is the percentage of 1000 amperes.

In Fig. 2 the terminal M when connected, results in zero induction in core because the impedances of paths B and C are then equal, Mo being so located in construction of the transformer. Should the impedances become unequal, either accidentally or by being intentionally made so, the fact is indicated by a deflection of meter 16. The amount of this deflection indicates the degree of unbalance in the impedance due to such accident or intentional alteration. A measure of the unbalance is obtained by placing a current meter 18 in the circuit A, I

fixing the value of the current a, and marking the scale in ammeter 16 in terms of the value of the condition producing the unbalance of resistance. Thus, path B may be placed in heat conducting relation to a heat source of high or low temperture so as to vary the resistance of path B in accord with such temperature, while path C may be placed in heat conducting relation to a heat source of low or high temperature, and meter 16 will then indicate the difference of temperature between the two sources of heat.

It will be readily appreciated that the polarity of the secondary winding 14 changes with respect to the polarity of the primary winding 12 as the current difference bc changes from plus to minus due to the changes in resistance of paths B and C. Therefore by connecting an alternating current wattmeter W so that the potential coil r receives energy from circuit A directly while the current coil s receives energy from the secondary winding 14", the direction of deflection of the indicator in the wattmeter indicates the path C or B having the predominant or larger value of current flowing.

In Fig. 2 the terminals M3 and M3, if so chosen, may

afford equal values of current at ammeter 16', but the I polarity of the current flowing in the secondary may be reversed with respect to the primary current by connecting circuit A to one or the other of M3 and M3.

It will be observed that the terminals M, M, P, etc., are offset from the main conductors 12 or 12. The effect is to prevent the connection to one of the terminals from having any substantial influence on the division of current in paths B and C, the current being uniformly distributed in the terminal before it enters the paths B and C.

The exact positioning of any particular terminal of the several terminals M0, M, M3, etc. determines the exact ratio of resistances of the paths, such as of paths B and C, and therefore the exact transformer ratio. Achieving any particular value of the ratio of resistances is facilitated by employing for each such terminal a terminal structure such as that illustrated in Fig. 4. In this figure one terminal P corresponds to terminal P in Fig. 1, and a second terminal To is shown to correspond to the terminal Mo of Fig. 2; that is, the intention is that paths B and C carry equal, or ascertainably nearly equal, currents and that therefore the resistances ratio of the paths shall be fixable at unity exactly, or at some exact value very near to unity. The structure of terminal To may be employed in place of any one or more of the 4 other terminals, as M4, M4 in Fig. 2, or M and M in Fig. 1.

The terminal T0 comprises two terminal lug parts 30 and 32 which are preferably rigidly integral with the metal of winding BC. The terminal lug parts 30 and 32 in Fig. 4 are placed roughly symmetrically with re spect to a section S from which section the resistances of paths B and C to'P are equal. When the same terminal structure is used for terminal M in Fig. 1, for example, the corresponding lug parts are placed roughly symmetrically with respect to a section in winding BC from which section the resistances in paths B and C to P are in the desired resistances ratio.

The terminal lug parts are preferably otherwise identical and each have parallel plane surfaces 34 and 36 between which surfaces each lug part is of substantial thickness and is rigid with the main body of the winding BC so as to not be bent out of position in ordinary use. The terminal lug parts 30 and 32 are perforated and threaded on a common axis preferably perpendicular to their surfacesfor the reception therethrough of a ratio adjustment terminal post 38 which comprises an externally threaded tubular portion of two parts 40 and 42 of like lengths respectively positioned in the lug parts 30 and 32 and extending between the lug parts and projecting substantial distances away from surfaces 36 so that throughout the range of adjustment the parts 40 and 42 engage all of the threads in the terminal lug parts 36 and 32 to effect a uniform area of contact equal in both lug parts. The tubular parts 40 and 42 have integrally joined thereto by a hub part 44 an axial conductor part 46 carrying a contact terminal 48 which is formed to constitute a slip ring and associated with which there is a current applying brush 50. A second axial part 52 of the terminal post 38 is provided as an adjustment drive shaft actuable in rotation by hand with a wheel handle part 54 of the post. It will be noted that, as shown, the hub part 44 joins conductor 46 to the threaded parts 40 and 42 about midway between the lug parts 30 and 32 and that the areas of engagement of the threads of parts 40 and 42 in lug parts 30 and 32 are substantially equal and the resistances of the lug parts between the threads and the main body of winding BC are nearly equal and preferably equal. Therefore, by adjusting theposition of the hub part 44 along the axis of threading rightward or leftward, the ratio of the resistances to current flow along paths B and C from contact terminal 48 and conductor 46 to terminal P may be adjusted to unity or to any of a range of desired values close to unity in the case supposed for Fig. 4, thus achieving ready precision adjustment. It will be observed that, with the conductor part 46 and the parts 40 and 42 ac curately machined to concentricity, the current distribution from 46 through 44 and 40 and 42 is as nearly as possible uniform and independent of rotary positions, and of the contact distribution on ring 48. The length of conductor 46 insures a uniform distribution of current over its cross section before the current reaches hub 44.

Prior to final adjustment of the ratio, the threaded parts are firmly locked together by lock nuts 56 hearing on the faces36 of the lug parts through an electrical insulator washer 58. Only one lock nut is illustrated;

one to be placed against face 36 of lug part 32 has been omitted from the drawing.

' It is believed to now be readily apparent that in order to adjust the effective ratio of the transformer, known current is applied at brush and terminal P, with a current meter in the circuit of secondary winding 14, while handle 54 is turned until the desired ratio of input to output current is established, after which the threaded parts are locked together and the ratio again checked; possibly release of the threads andreadjustment may be indicated to be necessary, and some adjustment is available by varying the tightness of the locking nuts.

I in making ratio ad ustments near the unity resistance ratio for paths B and C it is preferable to utilize a wattmeter arrangement as in Fig. 2 in order to fix the relative polarities of the output terminals with respect to the input terminals as desired. I Otherwise the relative polarities of an input and an output terminal may easily be made other than may be desired. I

By the arrangement of Fig. 3 the invention is adapted for use with the so-called split-core transformer. The

transformer core 20 and secondary winding 22 with instrument 24 are of known conventional design. The core provides hinged sections 20a and 20b split at 20c and hinged at 26d so that conductors may be slipped through the gap 200 when 20a and 20b are separated.

The primary winding is comprised of a plurality of conductors N1, N2 Nn where It may be any value, for example 200 conductors. These conductors may be flexible. The resistances of conductors N1, Nn may be all exactly equal but need not be. Preferably they are all bonded to the terminals U and V of the primary winding by welding or soldering so that the joints have in variable resistance. The value of the conductance or admittance between U and Vfor any conductor N then has a fixed value.

By choosing a group of N1, N2, Nx, conductors for threading through core 20 in one direction, and the balance of conductors for threading therethrough in the other direction, as shown, a certain percentage of the current a is effective to produce induction in core 20. This percentage is determined in calibrating the primary in advance for each combination of the conductors in the two groups. Thus this primary winding is applicable for employment with any split core type transformer irrespective of the induction at which it is designed to operate most accurately, because a value of induction is provided by the primary winding which conforms to that of the core.

In Fig. 5 an improved form of Fig. 3 arrangement is illustrated to comprise terminal disc plates U and V having axially integral therewith rod terminals 60. The several conductors N1, N2, etc., are preferably of equal length and resistances and are permanently electroconductively attached to the plates respectively at points radially equidistant from the terminal rods 60. The conductors N1 and N2 etc. are, moreover, of the extra flexiblevarietyso that they. can easily be formed by hand into loops as shown. Th seveml conductors are suitably covered with insulation so that current will i not interchange between them or bridge the loops. The

arrangement as described makes the resistances of all paths including separate conductors N equal between the ends of terminals 60 and 62.

In Fig. 5 the dash circle 64 represents the magnetic axis of the core of a split-core instrument transformer and it will be observed that all seven conductors pass through the core hole once only. However, assuming that the instantaneous current flow is from 62 to 60, the current flow is upward through the hole of the transformer in conductors N2 N6 inclusive but the current fiow is downward through the hole in conductors N1 and N7. Thus the efiective number of conductors is five minus two equals three.

It will be evident that the flexible conductors N may be temporarily tied in a position with certain ones in the loop form for the reception of the transformer core along path 64. It should be noted that the starting and ending f a loop will be on the outside of the ring core of the transformer, thus bringing the diametrically opposite part of the loop into a group with the unreversed conductors for encirclement by the core. By making the several conductors N of adequate length, a second combination of conductors including, say three looped conductors in Fig. 5, may be tied up at another longitudinal region between the terminals U and V for the reception of the core in their encirclement. Thus, but one conductor N would be efifective and a larger current may be measured using the same ring core transformer.

In Fig. 6 the invention is extended to utilization for the primary purpose of a bus bar and the secondary purpose of a means by which current may be measured in that bus bar, using but one split ring core measuring transformer for widely variant values of current traversing the section of bus bar. The material of the bus bar is of sufficient section transverse the bar length to retain adequately its shape in section. The bar is, of course of an electroconductive material. As shown a flat bar of uniform cross section from end to end is formed to provide terminal attachment parts 70 and 72 joined by parts 74 and 76 of substantial length to winding parts sets 78 and 80 and 82 and 84.

The winding parts 78 and 80 correspond respectively to the paths B and C of Fig. 1 and the central parts 78a and 89a are, in use, encircled by the split core of a measuring instrument, two large openings being formed through the winding as shown for this purpose. The parts 82 and 84 are similar to the parts 78 and 80 and the parts 82a and 84a are, in current measurements, encircled by the split core of the measuring instrument transformer. The difference in construction and effect of the two series related sets of windings is that due to the ratios of resistances in the paths of the sets. The ratio is, in each case, determined by the lateral position of a longitudinal slot cut through the bar between the parts of which the winding parts are subsequently reshaped as shown. Thus, prior to bending the bar parts 32 and 84, the bar is, while fiat slotted from 86 to 88, the slot being sufiiciently wide to insulate the parts between these points. The ratios of resistances for the different windings depend upon the relative distances from the center line of the bar to the slot center line, the slot being preferably of the same minimum width. The joining part 90 is made of sufficient length that the current is uniformly distributed before it enters one winding after leaving the other.

By the arrangements of Fig. 6 two widely variant values of current flowing in the bus at difierent times can be measured with one split core instrument having but one instrument circuit winding.

The transformer cores, in order to provide for a complete range of current measurement, are provided with multiple range primary winding 26 having several taps in the conventional manner. The rated value of current in each range of the primary winding produces the same value of induction in the core as a single turn primary winding produces at its rated current, and this is the value of the induction at which the paths B and C cause the core to operate when connected to operate for their rated values of currents. Accordingly, the core is operated at the same range of flux densities with the multiple turn self-contained primary winding, the single turn inserted or bar type winding, and the variable percentage efifective turn winding here introduced.

1 claim:

1. A. transformer comprising, in combination: a magnetizable core; a winding for said core comprising two terminal portions providing for the concurrent connection thereto of an external circuit; a plurality of conductors extending in electro-conductive parallelism between and electro-conductively permanently connected to the terminals, one of said conductors being linked with the core to magnetize it and another of the conductors being linked with the core to oppose the magnetization of the one conductor; one of said terminal portions providing a plurality of terminal connecting lugs each lug being dififerent spaced along one of said conductors from the other terminal portion than the corresponding spacing of any other lug for selection to provide corresponding fixed ratios of impedance between the parallel paths between the terminals.

2. A transformer having a core, a primary winding, and 'asecond winding, two connecting terminals on the primary windingythe primary winding providing two electro-conducting parallel paths for current between the two connecting terminals arranged to provide for differential magnetization of the core; and means including a plurality of connecting devices on one of the terminals differently spaced along one of said paths from the other terminal for connecting an external circuit to the terminals to provide either positive or negative polarity of the secondary Winding terminals with respect to the primary terminals at any instant.

3. A transformer comprising, in combination: a magnetizable core having a hole therethrough; a continuously'integral metallic closed winding loop for said core having a terminal thereon outside said hole in said core and providing two conductors extending from said terminal to and through the hole, one conductor in a direction opposite to the other and joining together outside the hole to there form a multiple terminal region; and a plurality of additional terminals on said terminal region and spaced along said loop so as to provide ditferent ratios of resistance for the two conductors one to the other, between said first terminal and any particular one of the additional terminals.

4. A transformer comprising a winding providing two terminal portions; a core having a hole therethrough, conductors extending from one terminal portion through said hole in opposite directions and extending thence to the second terminal portion; one of said terminal portions providing a plurality of terminal connection devices, each of said connection devices being located at a point such that the electrical resistance of said conductor in one of said directions from any one of said points to the other terminal portion is different in value from the electrical resistance of said conductor in the other of said directions from such any one of said points to said other terminal portion.

5. A transformer comprising, in combination: a magnetizable core; a winding for said core comprising two terminal portions providing for the connection thereto of an external circuit; a plurality of conductors extending in electro-conductive parallelism between the two terminal portions; one of said conductors extending about the core to magnetize it and the other extending about the core to oppose the magnetizing effect of the one conductor; and means for varying the relative impedances of 'the paths in the conductors, one-to the other, comprising a series of spaced apart lugs on one of the terminal portions, each of the lugs being differently spaced, along one of said conductors, from the other terminal portion so as to efiect different resistance ratios of the two paths, one to the other, from each lugto the other terminal portion.

6. In combination: a magnetizable core, a transformer primary winding and a secondary winding, the primary winding having electro-conductively parallel current conductors, one conductor being linked with the core to magnetize it and the other oppositely linked to oppose the magnetizing effect of the first conductor and the conductors having normally equal conductances so as to produce a zero magnetizing effect in the core when the impedances of the two-conductors are equal; a source of alternating current for energizing the primary winding; and an indicating instrument having a pointer and two coils for actuation of said pointer, one coil being connected for direct electrical energization by the source and the other coil being connected for energization from the secondary winding, so that the deflection of the pointer indicates which conductor carries the most current when the conductances of said conductors are not equal.

7. An instrument transformer adapted to have its primary winding placed in a circuit so that measurement of the electrical value of the secondary winding of the transformer is a measurement of the electrical value of the circuit, comprising: a transformer having a primary winding composed of two conductors adapted to be placed in parallel in such circuit, each of said conductors arranged to produce in said transformer a field which is in opposition to the field of the other conductor so that the magnetization of said transformer is the resultant, or differential, magnetization of such fields and so that said resultant is a measure of the electricity in such circuit, and said conductors forming a loop having three or more taps placed therealong so that the impedance of said conductors, one with respect to the other, may be varied; and said transformer having a secondary winding usable for determining the value of such resultant magnetization as a measure of the electricity in such circuit.

References Cited in the file of this patent UNITED STATES PATENTS 895,801 Schubert Aug. 27, 1906 2,181,644 Seifert Nov. 28, 1939 

